The present invention relates generally to liquid level indicators and controllers and, more particularly, to a method and system for detecting and cross-checking faulty sensors in liquid level indicators and controllers.
Liquid level indicators and controllers monitor the level of liquids in vessels, such as drums and tanks. The liquid level indicators and controllers then display the liquid level on indicating devices. In steam generating applications, the liquid level indicators and controllers distinguish between liquid and steam and, in non-steam generating applications, the indicators and controllers distinguish between liquid and air. In addition to indicating the liquid level, the liquid level indicators and controllers can actuate alarms, valves, pumps, and/or other electric controls at preset liquid levels.
Given the environment in which liquid level indicators and controllers operate, it is important for these indicators and controllers to be reliable. If any component in the liquid level indicator and controller is faulty, the liquid level information may not be correct. If the liquid level indicator and controller indicates that the liquid level is higher than it actually is, the indicator and controller may actuate an alarm or control when it should not be actuated. Conversely, if the liquid level indicator and controller indicates that the liquid level is lower than it actually is, the indicator and controller may not actuate an alarm or control when it should be actuated. In either case, the consequences can be quite severe. Therefore, a need exists for detecting and cross-checking faulty components in liquid level indicators and controllers.
The present invention provides a method and system for detecting and cross-checking faulty sensors in liquid level indicators and controllers. A liquid level indicator and controller in which one embodiment of the present invention operates includes a control unit for controlling the other components of the liquid level indicator and controller, sensors electrically connected to the control unit for sensing the level of a liquid in a vessel, and an indicating device electrically connected to the control unit for displaying the liquid level.
The control unit includes a processor, primary storage, a signal generator, a signal detector, and relays. The processor is electrically connected to the primary storage, the signal generator, the signal detector, the relays, and the indicating device. The primary storage includes a monitor and a fault detector. In one embodiment of the present invention, the monitor and the fault detector are software programs stored in the primary storage. The monitor and the fault detector are executed by the processor to control the components of the liquid level indicator and controller. Both the signal generator and the signal detector are electrically connected to each of the sensors.
In operation, the liquid level indicator and controller has two (2) basic modes. The first mode is a monitor mode. In this mode, the liquid level indicator and controller, under the control of the monitor, senses the liquid level in the vessel using the sensors and displays the liquid level on the indicating device. The second mode is a fault detection mode. In this mode, the liquid level indicator and controller, under the control of the fault detector, detects and cross-checks faulty sensors. If a faulty sensor is detected, the liquid level indicator and controller determines the type of fault, i.e., whether the sensor is open or shorted.